1. Technical Field
Various embodiments generally relate to a structure for reducing electromagnetic interference and an electronic device using the same, and more particularly, to an electromagnetic interference suppressing structure to which coplanar waveguides (CPQ) are applied and an electronic device having the same.
2. Related Art
With distribution and development of electronic devices such as computers, computer hosts, portable electronic appliances and mobile communication terminals which operate electronic systems, electronic operations of those devices are unavoidably influenced by an increased amount of electromagnetic interference (EMI) induced internally or from an external sources. Interference sources may be generated from external electronic devices or internal electrical circuits. Suppression targets of EMI are mainly divided into radiated electromagnetic interference and conducted electromagnetic interference. Since radiated EMI is transferred directly through an open space without needing a transmission medium, it may be generally suppressed by shielding, grounding, etc. Since conducted EMI transfers noise by a power source or a signal circuit, other circuits inside an electronic device and the circuits externally connected with the electronic device generate conducted EMI and may interfere with a signal circuit of the electronic device. Therefore, electromagnetic interference is an unavoidable problem in any electronic and electrical circuit regardless of its high speed digital design. In particular, a differential signal transmitted as high speed data has serious common mode noise which is generated during signal transmission. The electromagnetic interference generated from common mode noise exerts a substantial influence on a wireless communication system interfacing with a device or an appliance.
FIG. 1A is a diagram illustrating the electromagnetic interference exerted on an electronic device by an externally connected device and a wireless communication device. FIG. 1A depicts a notebook computer 111 as an example. The notebook computer 111 is influenced by not only the electromagnetic interference transferred through a port such as, a USB port from an externally connected device 113 but is also influenced by wireless electromagnetic interference from a mobile communication device 115 positioned close to the notebook computer 111. FIG. 1B is a diagram illustrating the electromagnetic interference exerted on an internal circuit of an electronic device by common mode noise, The drawing slows interference phenomena induced by crosstalk 121, bend 122, length mismatch 123 and layout requirement 124. All of these interference types exert an influence on a wireless transmission system, and accordingly, difficulties exist in transmitting and receiving wireless signals in a wireless communication module. Hence, it is necessary to suppress such interference.
In conventional art, a common mode choke element is disposed in an electrical circuit to suppress common mode noise. In this way, common mode noise is suppressed by reaching high induced resistance using a magnetic core of high magnetic permeability. However, the magnetic core of high magnetic permeability may not effectively retain high magnetic permeability during a high frequency period, therefore, a damping phenomenon occurs. This prevents a common mode choke element from effectively suppressing common mode noise during high speed data transmission.
According to conventional art, a filtering structure for suppressing common mode noise is formed in a region positioned under differential signal lines. In addition to forming filters such as a transverse filtering portion and an interframe filtering portion in a substrate on both sides of and under the differential signal lines, the filtering structure also includes a common mode filter which is formed in the substrate directly under the differential signal lines and connects the transverse filtering portion and the interframe filtering portion. FIG. 1C is a diagram illustrating a filtering structure when a differential signal transfers current, according to conventional art. Referring to FIG. 1C, since a common mode filter 103 directly below a differential signal line 101 separately increases a new interference source, discontinuity of a differential signal may result and the quality of a digital transmission signal may be degraded.